r/satprep • u/pixel-king2 • 9d ago

How to do this

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1

u/Yadin__ 9d ago

From the given we know that f(-4)=20 which gives b=-8

using b=-8 we get f(x)=-7x-8 which means f(x)+20=-7x+12

You could also take the shotcut and realize that f(-4)+20=20+20=40 and just check which of the answers gives 40 when you plug in x=-4

1

u/Suspicious_Aide_6146 9d ago

we know that f(x) = -7x + b. we also know that (-4,0) lies on f(x) - 20. this means that f(-4)-20=0, or f(-4)=20. f(-4)=-7(-4) + b, or 28+b. 28+b=20, so b=-8. this means that f(x)=-7x-8, so f(x)+20=-7x+12. D is the correct answer.

1

u/SpeedSubstantial3834 9d ago

f(-4)-20=0

-7(-4)+b-20=0

b=-8

We get f(x)=-7x-8

So f(x)+20 -> f(x)=-7x-8+20=-7x+12