登录
(4)当x= 3时,下列算式中,(
$A.x^2+9 B.5x+2 C.4x+3$
C
)的结果是15。$A.x^2+9 B.5x+2 C.4x+3$
答案
当x=3时，
A. $x^2 + 9 = 3^2 + 9 = 9 + 9 = 18$
B. $5x + 2 = 5×3 + 2 = 15 + 2 = 17$
C. $4x + 3 = 4×3 + 3 = 12 + 3 = 15$
C
A. $x^2 + 9 = 3^2 + 9 = 9 + 9 = 18$
B. $5x + 2 = 5×3 + 2 = 15 + 2 = 17$
C. $4x + 3 = 4×3 + 3 = 12 + 3 = 15$
C
(5)一台电视机的价格是5600元,比一台洗衣机的价格的2.5倍少15元。如果设一台洗衣机的价格是x元,那么根据题意正确的方程是(
A.2.5x-15= 5600
B.2.5x+15= 5600
C.(2.5+15)x= 5600
A
)。A.2.5x-15= 5600
B.2.5x+15= 5600
C.(2.5+15)x= 5600
答案
A
解析
设一台洗衣机的价格是$x$元，根据题意，电视机价格比洗衣机价格的$2.5$倍少$15$元，可列方程：$2.5x - 15 = 5600$。
A
A
4.看图列方程解答。
(1)
(2)
(1)
(2)
答案
(1)解：3x + 500 = 2000
3x = 2000 - 500
3x = 1500
x = 500
(2)解：x + (x + 6) = 36
2x + 6 = 36
2x = 36 - 6
2x = 30
x = 15
3x = 2000 - 500
3x = 1500
x = 500
(2)解：x + (x + 6) = 36
2x + 6 = 36
2x = 36 - 6
2x = 30
x = 15
5.解方程。
x+1.2= 9
13+2x= 28.5
9.8x+x= 75.6
x÷3.6= 0.5
x+1.2= 9
13+2x= 28.5
9.8x+x= 75.6
x÷3.6= 0.5
答案
x+1.2=9
解：x=9-1.2
x=7.8
13+2x=28.5
解：2x=28.5-13
2x=15.5
x=15.5÷2
x=7.75
9.8x+x=75.6
解：10.8x=75.6
x=75.6÷10.8
x=7
x÷3.6=0.5
解：x=0.5×3.6
x=1.8
解：x=9-1.2
x=7.8
13+2x=28.5
解：2x=28.5-13
2x=15.5
x=15.5÷2
x=7.75
9.8x+x=75.6
解：10.8x=75.6
x=75.6÷10.8
x=7
x÷3.6=0.5
解：x=0.5×3.6
x=1.8
