3% : 5% + 987% - 765% = 0,6% + 987% - 765%

                                     =        987,6% - 765%

                                     =              222,6%

a: \(=\left(\cos^215^0+\cos^275^0\right)+\left(\cos^225^0+\cos^265^0\right)+\left(\cos^235^0+\cos^255^0\right)+\cos^245^0\)

=1+1+1+1/2

=3,5

b: \(=\left(\sin^210^0+\sin^280^0\right)-\left(\sin^220^0+\sin^270^0\right)+\left(\sin^230^0\right)-\left(\sin^240^0+\sin^250^0\right)\)

=1-1-1+1/4

=-1+1/4=-3/4

c: \(=\left(\sin15^0-\cos75^0\right)+\left(\sin75^0-\cos15^0\right)+\sin30^0\)

=1/2

b)Thay (y-x)² bằng (x-y)², sau đó đặt nhân tử

e)Nhóm 3 số cuối vào 1 nhóm

f)Áp dụng HĐT thứ 3 bình thường

áp dụng công thức sin²a+cos²a=1

A= sin²a +cos²a-2sina.cosa-sin²a-cos²a+2sina.cosa = 0

B=(sỉn²a+cos²a)² =1² =1

C= cos²a(cos²a+sin²a)+ sin²a=cos²a+sin²a=1

D=sin²a(sin²p+cos²p)+cos²a=sin²a+cos²a=1

E= (sin²a+cos²a)(sin⁴a-sin²a.cos²a+cos⁴a)+3sin²a.cos²a

=sin⁴a+2sin²a.cos²a+ cos⁴a=(sin²a+cos²a)²=1

(1) => 2x²+2y²+2z²-2xy-2yz-2xz=0

<=> (x²-2xy+y²) + (x^2-2xz+z²) + (y²-2yz+z²)=0

<=> (z-y)² + (x-z)² + (y-z)² = 0

<=> x=y=z

(2) => x²⁰⁰²  + x²⁰⁰²  + x²⁰⁰² = 3²⁰⁰³

<=> 3x²⁰⁰² = 3²⁰⁰³

x=y=z=3

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