Question

a)Use substitution to solve the pair of equations below.x+ y = 72x –3y= 9

b)Solve the pair of equations below using elimination. x + 2y = -43x –5y= -1

Answer 1

$\Huge\boxed{\fcolorbox{violet}{pink}{Answer }} \dashrightarrow$

a) x + y = 72 - - - (i)

x - 3y = 9 - - - (ii)

x + y = 72 ---(i)

x = 72 - y ---(ii)

x - 3y = 9 --- (iii)

divide equation (iii) by 3

x - y = 3 ---(iv)

substitute ( x = 72 - y ) in equation (iii)

x - 3y = 9

72 -y - 3y = 9

72 - 4y = 9

4y = 72 - 9

4y = 63

y = 63/4

put y = 63/4 in equation (ii)

x = 72 - y

x = 72 - 63 /4

x = ( 74 × 4 ) -63/4

x = 225/4

b) x+ 2y = -43

x - 5y = -1

$\\ x \: + 2y = - 43 - - -(i) \\ x - 5y = - 1 - - - (ii) \\ \\ subtract \: eq ^{n} (i) and \: (ii) \\ \: \: x + 2y = - 43 \\ - \: \: \: \: x - 5y = - 1 \: \: \: \: \: \: \: \: \: \: \\ - - -- - -- - - \\ - 7y = 42 \\ y = \frac{42}{ - 7} \\ \large \boxed {y = - 6} \\ put \: y = - 6 \: in \: eq ^{n} (i) \\ x + 2y = - 43 \\ x + 2( - 6) = - 43 \\ x - 12 = - 43 \\ x = - 43 + 12 \\ \large \boxed{x = - 31}$

$\huge \orange \dagger \pink { \: thanks} \orange \smile$