Question

How do you solve –4x+7y=–10 and x–5y=9 using substitution?

Answer 1

Answer:

let -4x+7y=-10------------(i)

x-5y=9----------------------(ii)

multiply (ii) by (-4)

so it is

-4x+7y=-10----------(i)

-4x+20y=-36----------(ii)

subtract (ii) from (i)

x will be zero and y= -26

y=-26

put the value of y in (i)

-4x+7(-26)=-10

-4x-182=-10

-4x=182-10

-4x=172

x=172/-4

x=-43

now you have both x=-43 and y=26

for check you answer put these value in any equation from(i) and (ii) if you get the -10 from first and 9 from (ii) then the answer is correct.

Answer 2

-4x + 7y = -10

(or) 4x - 7y = 10 .....( i )

x - 5y= 9

(or) x = 9 + 5y .....( ii )

Substituting ( ii ) in ( i ), we get,

4( 9 + 5y ) - 7y= 10

36 + 20y - 7y = 10

36 + 13y = 10

13 y = -26

y = -2

Substitute the value of y in ( ii ),

x = 9 + 5y

x = 9 + 5(-2)

x = 9 - 10

x = -1