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If f(x)=2x2+5and g(x)=3x+a, find a so that the graph of f∘g crosses the y-axis at 23.

Short Answer

Expert verified

The value ofais±3.

Step by step solution

01

Step 1. Given Information

Given thatf(x)=2x2+5and g(x)=3x+a,value off∘gx=23atx=0.

02

Step 2. Solution

We know that f∘g(x)=f(g(x)).

Here, f(x)=2x2+5and g(x)=3x+a.

So, f∘g(x)=f(g(x))f∘g(x)=2(g(x))2+5 f∘g(x)=2(3x+a)2+5 f∘g(x)=2{9x2+6xa+a2}+5f∘g(x)=18x2+12xa+2a2+5

So, at x=0, f∘g(x)=23.

Now,

atx=0,f∘g0=18(0)2+12(0)(a)+2a2+523=0+0+2a2+52a2=18a2=9a=±3.

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