7. 下列各式中,不能用平方差公式计算的是().

A.$(-x-y)(x-y)$
B.$(-x+y)(-x-y)$
C.$(-x+y)(x+y)$
D.$(-x+y)(x-y)$

【点拨】本题考查平方差公式.
【解析】$(-x-y)(x-y)=-(x+y)(x-y)=-(x^2-y^2)=-x^2+y^2$,故A选项能用平方差公式计算;$(-x+y)(-x-y)=(-x)^2-y^2=x^2-y^2$,故B选项能用平方差公式计算;$(-x+y)(x+y)=-(x-y)(x+y)=-(x^2-y^2)=-x^2+y^2$,故C选项能用平方差公式计算;$(-x+y)(x-y)=-(x-y)(x-y)=-(x-y)^2=-x^2+2xy-y^2$,故D选项不能用平方差公式计算.故选 D.

8. 在下面的正方形分割方案中,可以验证$(a+b)^2=(a-b)^2+4ab$的图形是().
A. B. C. D.

【点拨】本题考查乘法公式的几何背景.
【解析】由选项A可得$a^2-b^2=(a+b)(a-b)$,$\therefore$选项A不符合题意;由选项B可得$(a+b)^2=a^2+2ab+b^2$,$\therefore$选项B不符合题意;由选项C可得$(a-b)^2=a^2-2ab+b^2$,$\therefore$选项C不符合题意;由选项D可得$(a+b)^2=(a-b)^2+4ab$,$\therefore$选项D符合题意.故选 D.

9. 计算 $ a^5 ÷ a $ 的结果等于 ______.
10. 数据 0.023 用科学记数法表示为 ______.
11. 如图,将 $ △ OAB $ 绕点 $ O $ 逆时针旋转 $ 70° $得到 $ △ OCD $,若 $ ∠ AOB = 40° $,则 $ ∠ AOD $ 的度数为 ______度.

9. $a^4$
【点拨】本题考查同底数幂的除法.
【解析】$a^5÷a=a^{5-1}=a^4$.故答案为$a^4$.
10. $2.3×10^{-2}$
【点拨】本题考查科学记数法的表示方法.
【解析】$0.023=2.3×10^{-2}$.故答案为$2.3×10^{-2}$.
11. 30
【点拨】本题考查旋转的性质.
【解析】$\because$将$△ OAB$绕点$O$逆时针旋转$70°$得到$△ OCD$,$\therefore∠ DOB=70°$.$\because∠ AOB=40°$,$\therefore∠ AOD=∠ BOD-∠ AOB=30°$.故答案为30.

$＜[EOG_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD76_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜$|card|$＞:＜[PAD_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD74_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜/seed:tool_call_never_used_51bce0c785ca2f68081bfa7d91973934＞＜[SOGP_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜$|FCResponseBegin|$＞＜[SOI_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[UNK_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜$|video|＞:＜RichMediaCreation＞＜|FCResponseBegin|$＞＜[PLHD89_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[SOG_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜/escapeShell＞＜[PLHD69_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD74_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜answer_never_used_51bce0c785ca2f68081bfa7d91973934＞＜[PLHD61_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜$|image|$＞:＜[botu_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD78_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜/function_never_used_51bce0c785ca2f68081bfa7d91973934＞＜[SPEAK_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD83_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜seed:tool_call_never_used_51bce0c785ca2f68081bfa7d91973934＞＜$|FCResponseBegin|$＞＜[PLHD76_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD82_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜/RichMediaReference＞＜[PLHD62_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD69_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD61_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[EOG_never_used_51bce0c785ca2f68081bfa7d91973934]＞$$＜parameter_never_used_51bce0c785ca2f68081bfa7d91973934=＜RichMediaShow＞$

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13. 若$x,y$是正整数,且$a^x=4,a^y=8$,则$a^{x+y}=$.

13. 32
【点拨】本题考查同底数幂的乘法法则.
【解析】$\because a^x=4$,$a^y=8$,$\therefore a^{x+y}=a^x·a^y=4×8=32$.故答案为32.

＜|card|$＞:＜[PLHD96_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD83_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜function_never_used_51bce0c785ca2f68081bfa7d91973934=＜seed:tool_call_never_used_51bce0c785ca2f68081bfa7d91973934＞＜answer_never_used_51bce0c785ca2f68081bfa7d91973934＞＜[PLHD95_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜/seed:tool_call_never_used_51bce0c785ca2f68081bfa7d91973934＞＜[PLHD78_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜/RichMediaReference＞$$＜[PLHD70_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD67_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[BOS_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜doubao_withdraw＞＜[PLHD55_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD82_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD98_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD62_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD97_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD87_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[SPEAK_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD78_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD79_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD89_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜/answer_never_used_51bce0c785ca2f68081bfa7d91973934＞＜[PLHD81_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜/reflection_never_used_51bce0c785ca2f68081bfa7d91973934＞＜[PLHD95_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜$|superscript|＞:＜|FCResponseBegin|$＞＜[EOGP_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD75_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD80_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[EOGP_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜/RichMediaCreation＞＜[botu_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD56_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜/answer_never_used_51bce0c785ca2f68081bfa7d91973934＞＜[PAD_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD88_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜/seed:tool_call_never_used_51bce0c785ca2f68081bfa7d91973934＞＜/doubaothinking_never_used_51bce0c785ca2f68081bfa7d91973934＞＜[EOI_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD65_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD55_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD87_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[SEP_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜/function_never_used_51bce0c785ca2f68081bfa7d91973934＞＜$|FCResponseBegin|$＞＜[PLHD70_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜$|video|$＞:＜[PLHD75_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD77_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜RichMediaReference＞＜doubaothinking_never_used_51bce0c785ca2f68081bfa7d91973934＞＜[PLHD76_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜hiddenthink＞＜$|superscript|$＞:＜[PLHD43_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD81_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[eotu_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD74_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD87_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜/parameter_never_used_51bce0c785ca2f68081bfa7d91973934＞＜[UNK_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD65_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[eou_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD58_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD62_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜RichMediaCreation＞$$＜/think_never_used_51bce0c785ca2f68081bfa7d91973934＞＜[PLHD58_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD57_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜/RichMediaCreation＞＜[PLHD86_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜/reflection_never_used_51bce0c785ca2f68081bfa7d91973934＞＜[PLHD78_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[SOGP_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜doubaothinking_never_used_51bce0c785ca2f68081bfa7d91973934＞＜RichMediaShow＞＜[PLHD68_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD64_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜$|paragraph|$＞:＜[SOI_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD56_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD58_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD93_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD92_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜hiddenthink＞＜[PLHD85_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[SOI_never_used_51bce0c785ca2f68081bfa7d91973934]＞$$＜[PAD_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD86_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜function_never_used_51bce0c785ca2f68081bfa7d91973934=＜/escapeShell＞＜[PLHD86_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜/function_never_used_51bce0c785ca2f68081bfa7d91973934＞＜[PLHD91_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD99_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[CLS_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜/reflection_never_used_51bce0c785ca2f68081bfa7d91973934＞＜$|superscript|＞:$＜reflection_never_used_51bce0c785ca2f68081bfa7d91973934＞＜$|image|$＞:＜[PLHD64_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD74_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD99_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜RichMediaShow＞＜[PLHD97_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[MASK_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD93_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD55_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜/reflection_never_used_51bce0c785ca2f68081bfa7d91973934＞＜[PLHD79_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD57_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[EOGP_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜RichMediaReference＞＜/answer_never_used_51bce0c785ca2f68081bfa7d91973934＞＜[PLHD43_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD84_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD62_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD100_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[SEP_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜RichMediaShow＞＜[UNK_never_used_51bce0c785ca2f68081bfa7d91973934]＞＜[PLHD59_never_used_51bce0c785ca2f68081bfa7d91973934]＞$

未检测到有效数学题干内容，请补充完整具体的题目条件与问题后，再进行对应规范解答。

16. 如图,把$△ ABC$沿线段$DE$折叠,使点$A$落在$BC$上的点$F$处,$BC// DE$,若$∠ B=50°$,则$∠ BDF=\_\_\_\_\_\_°$.

16. 80
【点拨】本题考查折叠问题与平行线的性质.
【解析】$\because BC// DE$,$∠ B=50°$,$\therefore∠ ADE=50°$.由折叠的性质得,$∠ ADE=∠ EDF=50°$,$\therefore∠ BDF=180°-50°-50°=80°$.故答案为80.

17. 已知 $ a - b = 4 $，则 $ a^2 - b^2 - 8a $ 的值为 ______。

17. -16
【点拨】本题考查平方差公式的应用.
【解析】$\because a-b=4$,$\therefore a^2-b^2-8a=(a+b)(a-b)-8a=4(a+b)-8a=4b-4a=-4(a-b)=-4×4=-16$.故答案为-16.

18. 如图,在长方形ABCD中,BC = a,AB = b(b ＜ a ＜ 2b),四边形ABEH和四边形ECGF都是正方形.当a,b满足的等量关系为时,图形是一个轴对称图形.

18. $a=\dfrac{3}{2}b$
【点拨】本题考查轴对称图形的性质.
【解析】$\because$当图形是一个轴对称图形时,必须满足$DG=CG=EC$,$\therefore GC=DG=\dfrac{1}{2}b$,$BE=b$,$EC=\dfrac{1}{2}b$,$\therefore a,b$满足的等量关系是$a=\dfrac{3}{2}b$.故答案为$a=\dfrac{3}{2}b$.