\(B=\left(1+\dfrac{sin^2a}{cos^2a}\right).cos^2a-\left(1+\dfrac{cos^2a}{sin^2a}\right).sin^2a\)
\(=\dfrac{\left(sin^2a+cos^2a\right)}{cos^2a}.cos^2a-\left(\dfrac{sin^2a+cos^2a}{sin^2a}\right).sin^2a\)
\(=1-1=0\)
Giúp mình vs chiều phải nộp bài rồi
a)C= \(4\cos^2\alpha-3\sin^2\alpha.cos=\frac{4}{7}\)
b)\(\cos^2\alpha+\cos^2\beta+\cos^2\alpha.\sin^2\beta+\sin^2\alpha\)
c)2\(\left(\sin\alpha-\cos\alpha\right)^2-\left(\sin\alpha+\cos\alpha\right)^2+\left(\sin\alpha.\cos\alpha\right)\)
d)\(\left(\tan\alpha-\cot\alpha\right)^2-\left(\sin\alpha+\cot\alpha\right)^2\)
Rút gọn biểu thức:
sin4\(\alpha\left(1+2\cos^2\alpha\right)+\cos^4\alpha\left(1+sin^2\alpha\right)\)
Đề bài: Tính giá trị:
O=\(\dfrac{\sin^2\alpha\left(1+\cos^3\alpha\right)\cos^2\alpha\left(1+\sin^2\alpha\right)}{\left(1+\cot^3\alpha\right)\left(1+\cot g^3\alpha\right)\sqrt{1+\cos^4\alpha}}\) với \(\cos^2\alpha=0,5678\)
P= \(\dfrac{\cot^2\alpha\left(1+\cos^3\alpha\right)+\cot g^2\left(1+\sin^3\alpha\right)}{\left(\sin^3\alpha+\cos^3\alpha\right)\left(1+\sin\alpha+\cos\alpha\right)}\) với\(\cot\alpha=\cot35^0.\cot36^0.\cot37^0....\cot52^0.\cot53^0\)
~~~ Các bn làm giúp mình nhé, thanks nhìu...!~~~
A = \(58\sin^6\alpha-87\sin^4\alpha+58\cos^6\alpha-87\cos^4\alpha\)
B = \(\left(\sin\alpha+\cos\alpha\right)^2-2\sin.\cos\alpha+3\)
Rút gọn
\(B=sin\alpha-sin\alpha.cos^2\alpha\)
\(C=\left(tg46^o+cotg46^o\right)-\left(tg46^o-cotg46^o\right)^2\)
CMR:\(1,\tan\alpha\cdot\cot\alpha=1\)
\(2,\sin^2\alpha+\cos^2\alpha=1\)
\(3,\tan\alpha=\dfrac{\sin\alpha}{\cos\alpha};\cot\alpha=\dfrac{\cos\alpha}{\tan\alpha}\)
Rút gọn biểu thức:
\(A=\dfrac{1+2sin\alpha.cos\alpha}{cos^2\alpha-sin\alpha}\)
Cho tam giác ABC vuông tại A có góc B>45o .Gọi M là trung điểm BC,đặt góc AMB =\(\beta\);góc C=\(\alpha\)
CMR: 1+ Sin\(\beta\)=\(\left(Sin\alpha+Cos\alpha\right)^2\)
Biết cot α=\(\sqrt{5}\). Tính giá trị biểu thức: A=\(\dfrac{\sin^2\alpha+\cos^2\alpha}{\sin\alpha.\cos\alpha}\)
