Đặt \(t=4sinx-3cosx=5\left(\frac{4}{5}sinx-\frac{3}{5}cosx\right)=5sin\left(x-\alpha\right)\)
\(\Rightarrow-5\le t\le5\)
Xét \(f\left(t\right)=t^2-4t+1\) trên \(\left[-5;5\right]\)
\(-\frac{b}{2a}=2\in\left[-5;5\right]\)
\(f\left(-5\right)=46\) ; \(f\left(2\right)=-3\); \(f\left(5\right)=6\)
\(\Rightarrow y_{min}=-3\) ; \(y_{max}=46\)
3. Tìm GTLN, GTNN:
a) \(y=2\sin^2x+3\sin x\cos x-2\cos^2x+5\)
b) \(y=\dfrac{3\sin x-\cos x+1}{\sin x-2\cos x+4}\)
c) \(y=\dfrac{2\left(x^2+6xy\right)}{1+2xy+y^2}\) biết x, y thay đổi thỏa mãn \(x^2+y^2=1\)
Tìm giá trị lớn nhất và giá trị nhỏ nhất của hàm số
a) \(y=f\left(x\right)=\dfrac{4}{\sqrt{5-2\cos^2x\sin^2x}}\)
b)\(y=f\left(x\right)=3\sin^2x+5\cos^2x-4\cos2x-2\)
c)\(y=f\left(x\right)=\sin^6x+\cos^6x+2\forall x\in\left[\dfrac{-\pi}{2};\dfrac{\pi}{2}\right]\)
giải phương trình
\(\sin x\sqrt{1+2\sin x}=\cos2x\)
\(\sin\left(\frac{5x}{2}-\frac{\pi}{4}\right)-\cos\left(\frac{x}{2}-\frac{\pi}{4}\right)=\sqrt{2}\cos\frac{3x}{2}\)
\(3\sqrt{\tan x+1}\left(\sin x+2\cos x\right)=5\left(\sin x+3\cos x\right)\)
\(\sqrt{2}\left(\sin x+\sqrt{3}\cos x\right)=\sqrt{3}\cos2x-\sin2x\)
\(\sin2x\sin4x+2\left(3\sin x-4\sin^2x+1\right)=0\)
Tìm GTLN, GTNN:
a, \(y=4\sin^2x-4\sin x+3\).
b, \(y=\cos^2x+2\sin x+2\).
c, \(y=\sin^4x-2\cos^2x+1\).
Giải PT
a) \(\left|\sin x-\cos x\right|+\left|\sin x+\cos x\right|=2\)
b) \(\tan x-3\cot x=4\left(\sin x+\sqrt{3}\cos x\right)\)
c) \(2\sin^2x-2\sqrt{2}\sin x+3\tan^22x-2\sqrt{3}\tan2x+2=0\)
1) sin\(\sin\left[\pi sin2x\right]\)=1
2) cos\(\left[\dfrac{\pi}{2}.cos\left(x-\dfrac{\pi}{4}\right)\right]\)=\(\dfrac{\sqrt{2}}{2}\)
3) sin(x+24*) + sin(x+144*) = cos20*
Tìm nghiệm của các phương trinh:
1,\(\left(sinx+\dfrac{sin3x+cos3x}{1+2sin2x}\right)=\dfrac{3+cos2x}{5}\)
2,\(48-\dfrac{1}{cos^4x}-\dfrac{2}{sin^2x}\left(1+cot2xcotx\right)=0\)
3,\(cos^4x+sin^4x+cos\left(x-\dfrac{\pi}{4}\right)sin\left(3x-\dfrac{\pi}{4}\right)-\dfrac{3}{2}=0\)
4,\(cos5x+cos2x+2sin3xsin2x=0\) trên \(\left[0;2\pi\right]\)
5,\(\dfrac{cos\left(cosx+2sinx\right)+3sinx\left(sinx+\sqrt{2}\right)}{sin2x-1}=1\)
6,\(\left(sinx+\dfrac{sin3x+cos3x}{1+2sin2x}\right)=\dfrac{3+cos2x}{5}\)
7,\(cos\left(2x+\dfrac{\pi}{4}\right)+cos\left(2x-\dfrac{\pi}{4}\right)+4sinx=2+\sqrt{2}\left(1-sinx\right)\)
Giải PT
a1) \(3.\cos4x-2^{ }\cos^23x=1\)
a2) \(2\cos2x-8\cos x+7=\dfrac{1}{\cos x}\)
a3) \(\dfrac{\left(1+\sin x+\cos2x\right)\sin\left(x+\dfrac{\pi}{4}\right)}{1+\tan x}=\dfrac{1}{\sqrt{2}}\cos x\)
a4) \(9\sin x+6\cos x-3\sin2x+\cos2x=8\)
1. CM:
\(\dfrac{1}{2}\le\dfrac{\sin x+2\cos x+3}{2\sin x\cos x+3}\le2\)
2. Giải PT:
a) \(\dfrac{1}{\cos x}=4\sin x+6\cos x\)
b) \(\sin^3\left(x-\dfrac{\pi}{4}\right)=\sqrt{2}\sin x\)
c) \(\dfrac{1}{\cos x}+\dfrac{1}{\sin2x}=\dfrac{2}{\sin4x}\)