Tìm cực trị của các hàm số sau:
a) y= x^3 -3x^2+9x+7
b) y=-5x^3+3x^2-4x+5

Okay, so you what you would is solve one equation for Y=mx+b and then substitute this equation for Y so the answer would be Y=-3/2x + 20
And then you would do 2x-3(-3/2x+20)=-11 and you solve it for x
But to get y you would substitute what you got for x into ether equations.