Question

If 10y = 7x - 4 and 12x + 18y = 1 ; find the value of 4x + 6y and 8y - x.

Answer 1

10y = 7x - 4    ........(1)
12x + 18y = 1 ........(2)
Multiplying (1) by 9 and (2) by 5, we get,
63x - 90y = 36 ........(3)
60x + 90y = 5 ........(4)
Adding (3) and (4), we get,
123x = 41
⇒ x = `(41)/(123) = (1)/(3)`

∴ 10y = `(7)/(3) - 4`

= `(7 - 12)/(3)`

= `(-5)/(3)`

⇒ y = `(-5)/(3) xx (1)/(10)`

= `(-1)/(6)`

∴ 4x + 6y = `(4)/(3) - 1`

= `(1)/(3)`

8y - x 
= `(-8)/(6) - (1)/(3)`

= `(-8 - 2)/(6)`

= `(-10)/(6)`

= `(-5)/(3)`.