Question

Không dùng máy tính hãy tính:

A= Sin²10⁰+Sin²20⁰+Sin²45⁰+Sin²70⁰+Sin²80⁰

B=Sin²42⁰+Sin²43⁰+Sin²44⁰+Sin²45⁰+Sin²46⁰+Sin²47⁰+Sin²49⁰

C= tan35⁰*tan40⁰*tan45⁰*tan50⁰*tan55⁰( dấu "*" là nhân nha)

D= cos²15⁰-cos²25⁰+cos²35⁰-cos²45⁰+cos²55⁰-cos²65⁰+cos²75⁰

Giúp mình nha!

Answer 1

a: \(=\left(sin^210^0+sin^280^0\right)+\left(sin^220^0+sin^270^0\right)+sin^245^0\)

\(=1+1+\dfrac{1}{2}=\dfrac{5}{2}\)

b: \(=\left(sin^242^0+sin^248^0\right)+\left(sin^243^0+sin^247^0\right)+...+sin^245^0\)

=1+1+1+1/2

=3,5

c: \(=tan35^0\cdot tan55^0\cdot tan40^0\cdot tan50^0\cdot tan45^0=1\)

d: \(=\left(cos^215^0+cos^275^0\right)-\left(cos^225^0+cos^265^0\right)+\left(cos^235^0+cos^255^0\right)-\dfrac{1}{2}\)

=1-1+1-1/2

=1/2