Question

17. The values of x and y in the pair of
equation 2x - 5y = 12 and 7x + 5y = 15 is​

Answer 1

By Elimination Method

2x-5y = 12 equation 1

7x+5y = 27

Cut 5y

9x = 27

x = 3

Put x in equation 1

2(3) -5y = 12

6 -5y = 12

-5y = 6

y = 6/-5

X = 3

Y = 6/-5

Answer 2

Given,

$\[2x - 5y = 12\]$--------(1)

$\[7x + 5y = 15\]$--------(2)

Solution,

Put the value of x from equation 1 into equation 2,

$\[\begin{array}{l}7x + 5y = 15\\ \Rightarrow 7\left( {\frac{{12 + 5y}}{2}} \right) + 5y = 15\\ \Rightarrow 84 + 35y + 10y = 30\\ \Rightarrow 45y = - 54\\ \Rightarrow y = - 1.2\end{array}\]$

Put the value of y into equation 1,

$\[\begin{array}{l}2x - 5y = 12\\ \Rightarrow 2x - 5 \times \left( { - 1.2} \right) = 12\\ \Rightarrow 2x + 6 = 12\\ \Rightarrow 2x = 6\\ \Rightarrow x = 3\end{array}\]$

Hence the values of x and y is $\[3\]$ and $\[ - 1.2\]$.