- Nhập \(sin^2\left(20^o\right)+sin^2\left(30^o\right)+sin^2\left(40^o\right)+sin^2\left(50^o\right)+sin^2\left(60^o\right)+sin^2\left(70^o\right)\)

vào màn hình bấm \(=3\)

- Nhập \(sin^2\left(36^o\right)+sin^2\left(54^o\right)-2tan\left(25^o\right).tan\left(65^0\right)\)vào màn hình bấm \(=-0,6031977533\)

Để mình giúp@Trịnh Ngọc Hân cho :

\(\sin\left(20^0\right)^2+\sin\left(30^0\right)^2+\sin\left(40^0\right)^2+\sin\left(50^0\right)^2+\sin\left(60^0\right)^2+\sin\left(70^0\right)^2+\sin\left(36^0\right)^2+\sin\left(54^0\right)^2-2\tan25^0.\tan65^0\)

\(=\left(\sin\left(20^0\right)^2+\sin\left(70^0\right)^2\right)+\left(\sin\left(30^0\right)^2+\sin\left(60^0\right)^2\right)+\left(\sin\left(40^0\right)^2+\sin\left(50^0\right)^2\right)+\left(\sin\left(36^0\right)^2+\sin\left(54^0\right)^2\right)-2\tan25^0.\tan65^0\)

\(=1+1+1+1-2.1=2\)

Học tốt !

= sin²20 + sin²30+sin²40+cos²40+cos²30+cos²20
= ( sin²20+cos²20)+(sin²30+cos²3)+(sin²40+cos²40)
= 1+1+1=3

a: 

b: \(B=3-sin^290^0+2\cdot cos^260^0-3\cdot tan^245^0\)

\(=3-1+2\cdot\left(\dfrac{1}{2}\right)^2-3\cdot1^2\)

\(=2-3+2\cdot\dfrac{1}{4}=-1+\dfrac{1}{2}=-\dfrac{1}{2}\)

c: \(C=sin^245^0-2\cdot sin^250^0+3\cdot cos^245^0-2\cdot sin^240^0+4\cdot tan55\cdot tan35\)

\(=\left(\dfrac{\sqrt{2}}{2}\right)^2+3\cdot\left(\dfrac{\sqrt{2}}{2}\right)^2-2\cdot\left(sin^250^0+sin^240^0\right)+4\)

\(=\dfrac{1}{2}+3\cdot\dfrac{1}{2}-2+4\)

\(=2-2+4=4\)

A=(sin​​​²20°+sin²70°)+(sin²30°+sin²60°)

+(sin²40°+sin²50°)-tan²45°

=(sin​​²20°+cos​²20°)+(sin²30°+cos²30°)+(sin²40°+cos²40°)-1

=1+1+1-1=2

kết quả là 2

\(A=sin42^0-cos48^0=cos\left(90^0-42^0\right)-cos48^0=cos48^0-cos48^0=0\)

\(B=cot56^0-tan34^0=tan\left(90^0-56^0\right)-tan34^0=tan34^0-tan34^0=0\)

\(C=sin30^0-cot50^0-cos60^0+tan40^0\)

\(=cos\left(90^0-30^0\right)-tan\left(90^0-50^0\right)-cos60^0+tan40^0\)

\(=cos60^0-tan40^0-cos60^0+tan40^0=0\)

\(A=\sin42^0-\cos48^0=\sin42^0-\sin42^0=0\)

\(B=\cot56^0-\tan34^0=\tan34^0-\tan34^0=0\)

a: \(cos70=sin20\)

20<25

=>\(sin20< sin25\)

=>\(cos70< sin25\)

b: \(\dfrac{sin50}{cos40}=\dfrac{cos\left(90-50\right)}{cos40}=\dfrac{cos40}{cos40}=1\)

a) Ta có: 

\(cos70^o=sin\left(90^o-70^o\right)=sin20^o\)

Ta so sánh \(sin25^o\) và \(sin20^o\)

\(25^o>20^o\Rightarrow sin25^o>sin20^o\)

\(\Rightarrow sin25^o>cos70^o\)

b) \(\dfrac{sin50^o}{cos40^o}\)

Ta có: 

\(cos40^o=sin\left(90^o-40^o\right)=sin50^o\)

\(\Rightarrow\dfrac{sin50^o}{cos40^o}=\dfrac{sin50^o}{sin50^o}=1\)

đáp án

A=Sin 42^o - cos 48^o =cos(90^o - 42^o) - cos 48^o= cos48^o - cos48^o=0

hok tốt

B=cos56^o-tan34^o=tan(90^o - 56^o) - tan34^o=tan34^o - tan34^o=0

Ta có: \(\tan^240^0\cdot\sin^250^0-3+\left(1-\sin40^0\right)\left(1+\sin40^0\right)\)

\(=\tan^240^0\cdot\cos^240^0-3+1-\sin^240^0\)

\(=-2\)