for such qns...this is the standard approach,,,,,,,
xonsider the eqn. f(x)=.a0x + a1x^2+a2x^3....................
its simple application of mean value theorem...
f(0)=f(1)=0
since the function is continuous and differentaible in (0,1)
there lies atleat one c in (0,1) such that f'(c) = 0
proved