Trova numeri

168 a

k/2 = -1

k = -2 = 1/3-x 

x-2 = 1/3

x = 2+1 = 7/3

verifica ;

1/2(1/3-7/3 = -1

1/2*-2 = -1

-1 = -1  OK !!

168 b

5k/2 = 1/4

k = 1/10 = 7/5-x 

x = 7/5-1/10 = 13/10

verifica ;

5/2(7/5-13/10) = 1/4

5/2*1/10 = 1/4

1/4 = 1/4  OK !!

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168/a)

$\small \dfrac{1}{2}·\left(\dfrac{1}{3}-x\right) = -1$

$\small \dfrac{1}{3}-x = -2$

$\small 1-3x = -6$

$\small -3x = -6-1$

$\small -3x = -7$

$\small \dfrac{\cancel{-3}x}{\cancel{-3}} = \dfrac{-7}{-3}$

$\small x= \dfrac{7}{3}$

168/b)

$\small \left(\dfrac{7}{5}-x\right)·\dfrac{5}{2} = \dfrac{1}{4}$

$\small \left(\dfrac{7}{5}-x\right)·10 = 1$

$\small \dfrac{70}{5}-10x = 1$

$\small 70-50x = 5$

$\small -50x = 5-70$

$\small -50x = -65$

$\small \dfrac{\cancel{-50}^{10}x}{\cancel{-5}_1} = \dfrac{-65}{-5}$

$\small 10x = 13$

$\small x= \dfrac{13}{10}$