(cosα)^2=( 1+cos2α)/2

(sinα)^2=( 1-cos2α)/2

(tan α) 2 = (1-cos2alpha)/(1+cos2alpha) The derivation formula is as follows.

The direct application of the double-angle formula is to raise the power, and the formula Cos2α can be deformed to get the formula of decreasing the power:

cos2α=(cosα)^2-(sinα)^2=2(cosα)^2- 1= 1-2(sinα)^2

cos2α=2(cosα)^2- 1,(cosα)^2=(cos2α+ 1)/2

cos2α= 1-2(sinα)^2,(sinα)^2=( 1-cos2α)/2

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a & gt0，b & gt0，2 \ {[ 1 \ a]+[ 1/b]} & lt； = radical sign [ab] < = [a+b]/2 <; = radical sign {[A 2+B 2]/2}

2.ab & lt={[a+b]/2}^2<； =[a^2+b^2]/2

3. Cauchy, [a1b1+a2b2+a3b3] 2

4.a、b、c & gt0，a+b+c & gt； =3× cubic radical sign [ABC], a 3+b 3+c 3 > =3abc

5.a, b>0, m, n m and n are all positive integers, and a [m+n]+b [m+n] > = a m× b n+a n× b m.

6. Absolute value of A+B

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