Bài 30 (SBT trang 196)

Chứng minh rằng :

a) \(\sin\left(270^0-\alpha\right)=-\cos\alpha\)

b) \(\cos\left(270^0-\alpha\right)=-\sin\alpha\)

c) \(\sin\left(270^0+\alpha\right)=-\cos\alpha\)

d) \(\cos\left(270^0+\alpha\right)=\sin\alpha\)

Bài 29 (SBT trang 195)

Tính các giá trị lượng giác của cung \(\alpha\), biết :

a) \(\sin\alpha=0,6\) khi \(0< \alpha< \dfrac{\pi}{2}\)

b) \(\cos\alpha=-0,7\) khi \(\dfrac{\pi}{2}< \alpha< \pi\)

c) \(\tan\alpha=2\) khi \(\pi< \alpha< \dfrac{3\pi}{2}\)

d) \(\cot\alpha=-3\) khi \(\dfrac{3\pi}{2}< \alpha< 2\pi\)

Bài 27 (SBT trang 195)

Hãy xác định dấu của các tích (không dùng bảng số và máy tính)

a) \(\sin110^0\cos130^0\tan30^0\cot320^0\)

b) \(\sin\left(-50^0\right)\tan170^0\cos\left(-91^0\right)\sin530^0\)

Bài 26 (SBT trang 195)

Hãy viết theo thứ tự tăng dần các giá trị sau ( không dùng bảng số và máy tính) :

a) \(\sin40^0,\sin90^0,\sin220^0,\sin10^0\)

b) \(\cos15^0,\cos0^0,\cos90^0,\cos138^0\)

Tìm số nguyên n thỏa mãn từng điều kiện sau:

a) (n+1)(n+3)=0

b) (|n|+2)(n²-1)=0

Cho x,y,z là ba số không âm thỏa mãn: x + y + z = 1. Chứng minh rằng:

\(\frac{x}{1+x^2}+\frac{y}{1+y^2}+\frac{z}{1+z^2}\le\frac{9}{10}\)

giải bất phương trình sau:

\(\left|\frac{5}{x+2}\right|< \left|\frac{10}{x-1}\right|\)

(nói rõ cách giải giúp mình, vì có nhiều chỗ mình chưa hiểu)

Giải các Phtr sau ☘Tiểu Tuyết☘

a) 26x3 - 12x2 + 13x = 6

b) (x + 1)3 - ( x - 1)3 = 6 ( x2 + x + 1)

c) \(\frac{3x-1}{x-1}-\frac{2x+5}{x+3}-\frac{8}{x^2+2x-3}=1\)

Tính nhanh

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bai giai