Let f(x)=2x? +1. Find f (3x+1)-f (x) = 2 (3x+1)? + 1 - ( 2x？ + 1 ) = 2(9x？ +6x+ 1) - 2x？ - 1 = 18x？ + 12x + 2 - 2x？ - 1 = 16x？ +12x+ 1 Let f(x)=-x? +x+2。 Find f (x+1)+f (x-1) =-(x+1)? +(x+ 1)+2 + [ -(x- 1)？ +(x- 1)+2 ] = -(x？ + 2x + 1) + 2 + [ -(x？ - 2x + 1) + 2 ] = -x？ - 2x - 1 + 2 + [ -x？ + 2x - 1 + 2 ] = -x？ - 2x + 1 -x？ + 2x + 1 = -2x？ +2 If f(x- 1)=2x? -4 times

Find f(x) f(x- 1)=2x? -4x = 2x？ - 4x + 2 - 2 = 2(x？ - 2x + 1) - 2 = 2(x- 1)x？ - 2 == >f(x) = 2x？ -2 2014-03-04 23:18: 21supplement: let f(x)=x? 5. If f(k)=k+ 1.

Find the value of k f(k) = k? - 5 = k + 1 == >k？ -k-6 = 0 (k-3) (k+2) = 0 k = 3 or k =-2 2014-03-04 23: 30:17 Supplement: If f(x- 1)=2x? -4 times

Find f(x) f(x- 1)=2x? -4x = 2x？ - 4x + 2 - 2 = 2(x？ - 2x + 1) - 2 = 2(x- 1)？ -2 The above figures are incorrect: = 2(x- 1)x? - 2 == >f(x) = 2x？ - 2