Question

Diket y=ax^2 + bx + 15. Jika gradien garis singgung di x=1 adalah 10 dan di x=3 adalah 18,maka nilai a-b = ?

Answer 1

Y' = 2ax + b
y'(1) = 2a + b = 10
y'(3) = 6a + b = 18
---Eleminasi---
-4a=-8
a= 2
2.2 + b = 10
b = 6

a-b = 2-6 = -4

Answer 2

Y = ax²+bx+15
m = 2ax + b
10 = 2a + b
18 = 6a + b -
 -8 = -4a
a = -8/-4 = 2
2a + b = 10 ⇔ 4 + b = 10 maka b =6
a - b = 2 - 6 = -4