Answer
a. $-2$
b. $ y=-2x-1$
Work Step by Step
Given $ y=x^2-4x, P(1,-3)$
a. slope=$\frac{(1+h)^2-4(1+h)-1^2+4\times1}{h}=\frac{2h+h^2-4h}{h}=-2+h=-2$ (as $h$ approach zero)
b. tangent line: $ y+3=-2(x-1)$, which gives $ y=-2x-1$
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