设f(x)在[a,b)]上连续且非负,试证∫abf(x)dx=0的充要条件是在[a,b]上f(x)≡0.
证 充分性是显然的,以下证明必要性.
试证明:
设fn∈C(1)((a,b))(n=1,2,…),且有
,, x∈(a,b).
若存在f'(x),F(x)在(a,b)上连续,则f'(x)=F(x),x∈(a,b).
设函数f(x)在[0,1]上连续,在(0,1)内可导且f(0)=f(1)=0,f(1/2)=1,试证明至少存在一点ξ∈(0,1),使得f`(ξ)=1.
设f(x)在[a,b]上连续,x1,x2,x3.xn∈[a,b],且t1+t2+t3+.+tn=1,ti>0,i=1,2,3...,n.证明:存在x0∈[a,b],使得f(x0)=t1f(x1) + t2f(x2) + .+ tnf(xn).
利用归结原则证明:lim n→无穷 (1+1/n+1/n^2)^n=e.
设f(x)及g(x)在[a,b]上连续,证明:
(1)若在[a,b]上,f(x)≥0,且则在[a,b]上f(x)≡0;
(2)若在[a,b]上,f(x)≥0,且f(x)≠0,则;
(3)若在[a,b]上,f(x)≤g(x),且则在[a,b]上f(x)≡g(x)。
设f(x)在[0,1]上连续,在(0,1)内可导,且f(0)=0证明:如果f(x)在(0,1)内不恒等于零,则必定存在一点ξ∈(0,1),使f(ξ)·f'(ξ)>0
试证明柯西积分判别法
设f(x)在x≥1上非负、连续且单调减,则级数∑n=1+∞f(n)与广义积分∫1+∞f(x)dx同敛散.
设f(x)及g(x)在[a,b]上连续,证明:
(1)若在[a,b]上, f(x)≥0,且 ∫baf(x)dx=0,则在[a, b]上,f(x)= 0;
(2)若在[a,b]上,f(x)≥0,且f(x)≠0,则∫baf(x)dx>0;
(3)若在[a,b]上,f(x)≥g(x),且∫baf(x)dx=∫bag(x)dx,.则在[a,b]上f(x)=g(x)
设f(x)及g(x)在[a,b]上连续,证明
(1)若在[a,b]上,f(x)≥0,且f(x)dx= 0,则在[a,b]上f(x)=0;
(2)若在[a,b]上,f(x)≥0,且f(x)≠0,则f(x)dx>0;
(3)若在[a,b]上,f(x)≤g(x),且f(x)dx=g(x)dx, 则在[a,b]上f(x)=g(x).