Question

solve each of the following equations by eliminating X (by substitution) (2) 4x-7y=23 5x+2y=-25

Answer 1

4x-7y= 23....(1)
5x+2y= -25.....(2)

Multiply ep no. 1 by 5 on both the sides..
5(4x-7y)= 5×23
20x- 35y = 115
Now, multiply ep no. 2 by 4 on both the sides so we will get the same values of x
4(5x+2y)= - 25
20x +8y= -100
Now, 20x-35y= 115. ..............1.
20x +8y= -100 ..............2.
(-). (-). (+). : (Changed the signs
= 0 -43y= 215 In order to cancel
Y= 215/-43 the x values)
Y = -5
Now put the value of y in any of the eqs. Either 1. Or 2.....i will prefer 2,
So on putting the value of y in eq no. 2 i will get,
5x +2y = -25. .........from eq..2.
5x +2(-5) = -25
5x -10= -25
5x= -15
x= -3.....