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15. $5x+15x$
$=( \quad + \quad )x$
$=20x$
$5ab-2ab+ab$
$=( \quad - \quad + \quad )ab$
$=( \quad )$
$=( \quad + \quad )x$
$=20x$
$5ab-2ab+ab$
$=( \quad - \quad + \quad )ab$
$=( \quad )$
答案
5x+15x
=(5 + 15)x
=20x
5ab-2ab+ab
=(5 - 2 + 1)ab
=4ab
=(5 + 15)x
=20x
5ab-2ab+ab
=(5 - 2 + 1)ab
=4ab
16. 当$x=10$时,表达式$(5x+0.5)$的结果是()。
答案
50.5
解析
当$x=10$时，
$5x + 0.5 = 5×10 + 0.5 = 50 + 0.5 = 50.5$
$5x + 0.5 = 5×10 + 0.5 = 50 + 0.5 = 50.5$
17. $\dfrac{3y+1}{3}=\dfrac{7+y}{6}$
解:$6×\dfrac{3y+1}{3}=\dfrac{7+y}{6}×6$
$\dfrac{x}{3}-\dfrac{x-6}{12}=2-\dfrac{2}{3}x$
解:$(\dfrac{x}{3}-\dfrac{x-6}{12})×\_\_\_\_\_\_=(2-\dfrac{2}{3}x)×\_\_\_\_\_\_$
解:$6×\dfrac{3y+1}{3}=\dfrac{7+y}{6}×6$
$\dfrac{x}{3}-\dfrac{x-6}{12}=2-\dfrac{2}{3}x$
解:$(\dfrac{x}{3}-\dfrac{x-6}{12})×\_\_\_\_\_\_=(2-\dfrac{2}{3}x)×\_\_\_\_\_\_$
答案
解：$(\dfrac{x}{3}-\dfrac{x-6}{12})×12=(2-\dfrac{2}{3}x)×12$
$4x - (x - 6) = 24 - 8x$
$4x - x + 6 = 24 - 8x$
$3x + 6 = 24 - 8x$
$3x + 8x = 24 - 6$
$11x = 18$
$x = \dfrac{18}{11}$
$4x - (x - 6) = 24 - 8x$
$4x - x + 6 = 24 - 8x$
$3x + 6 = 24 - 8x$
$3x + 8x = 24 - 6$
$11x = 18$
$x = \dfrac{18}{11}$
