Question

if f(x)=3x2-5x+7,show that f(-1)=3f(1)

Answer 1

TO PROVE: f(-1)=3f(1)
f(x)=3x^2-5x+7
f(1)=3(1)^2-5(1)+7
=3-5+7
=10-5
=5
f(-1)=3(-1)^2-5(-1)+7
=3(1)+5+7
=15
therefore,
f(-1)=3f(1)
15=3(5)
15=15
HENCE ITS PROVED

Answer 2

Friend,
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Question:If f(x)=3x2-5x+7,show that f(-1)=3f(1)

Solution:

So we here have the equation 

f(x) = 3$x^{2}$  - 5x + 7


So inorder to prove something lets find what is it first.

So we will find f(-1)?

So inorder to find f(-1) lets first understand what do we mean by f(-1)

We know that f(x) = 3$x^{2}$ -  5x + 7 

So in the case of f(-1) x is replaced by -1  so we here know what is f(x)
equals so in the place of x we will substitue -1.

f(x) = 3$x^{2}$ -  5x + 7 

f(-1) = 3( $-1^{2}$) - 5( -1) + 7

        = 3 + 5 + 7 

         =   15

so this is LHS

Now  lets find what is RHS.

So we will find 3f(1)?

So inorder to find 3f(1) lets first understand what do we mean by 3f(1)

We know that f(x) = 3$x^{2}$ -  5x + 7 

So in the case of 3f(1) x is replaced by 1  so we here know what is f(x)
equals so in the place of x we will substitue 1. and we will multiply the value by 3.

So

3f(1) = 3(3 -5 +7)

        =  3( 5)

         = 15

So RHS equals 15

since LHS = RHS  the above is proved.

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 hope this helps

regards