Explanation: using the substitution method y = x − 5 → ( 1 ) y = − 2 x + 4 → ( 2 ) since both equations are expressed in terms of x we
can equate them ⇒ x − 5 = − 2 x + 4 add 2x to both sides 2 x + x − 5 = − 2 x + 2 x + 4 ⇒ 3 x − 5 = 4 add 5 from both sides 3 x + 5 − 5 = 4 + 5 ⇒ 3 x = 9 divide both sides by 3 3 x 3 = 9 3 ⇒ x = 3 substitute this value in ( 1 ) y = 3 − 5 = − 2 As a check substitute these values into ( 2 ) right = − 6 + 4 = − 2 = left ⇒ point of intersection = ( 3 , − 2 )
After h hours A has 6000 - 2000h cells and B has 2000 - 1000h. Equating them as one form: 6000 - 2000h = 2000 - 1000h -2000h + 1000h = 2000 - 6000 -1000h = -4000 h = -4000/-1000 = 4 hours