Where is (\cot x) undefined?
(\cot x=\frac{\cos x}{\sin x}), so it is undefined when (\sin x=0). Always check the denominator carefully.
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SubjectsMathematics
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(\cot x=\frac{\cos x}{\sin x}), so it is undefined when (\sin x=0). Always check the denominator carefully.
View question details(\sec x=\frac{1}{\cos x}), so it is undefined when (\cos x=0). In reciprocal functions, the denominator cannot be zero.
View question details(\cosec x=\frac{1}{\sin x}), so it is undefined when (\sin x=0). In a reciprocal, the denominator function must not be zero.
View question detailsUsing (\sin^2 x+\cos^2 x=1), (\cos x=\frac{4}{5}). In the first quadrant, (\cos x) is positive.
View question detailsFrom (\sin^2 x=1-\cos^2 x), (\sin x=\frac{5}{13}). In the first quadrant, the positive value is taken.
View question detailsUsing (\sec^2 x=1+\tan^2 x), (\sec x=\frac{25}{24}). In the first quadrant, (\sec x) is positive.
View question detailsFrom (\cosec^2 x=1+\cot^2 x), (\cosec x=\frac{17}{15}). Take the positive value in the first quadrant.
View question details(\pi+x) lies in the third quadrant and (\sin x) is negative there. Hence (\sin(\pi+x)=-\sin x).
View question details(\pi+x) is in the third quadrant and (\cos x) is negative there. Therefore, (\cos(\pi+x)=-\cos x).
View question detailsThe correct identity is (1+\tan^2 x=\sec^2 x). In identity-based questions, check signs and fractions carefully.
View question detailsSquaring both sides gives (1+2\sin x\cos x=2). Hence (\sin x\cos x=\frac{1}{2}); squaring is useful in such questions.
View question detailsBy definition, \(\tan x=\frac{\sin x}{\cos x}\). Since \(\tan x=2\) is given, \(\frac{\sin x}{\cos x}=2\). The value \(\frac{1}{2}\) is the reciprocal and represents \(\cot x\), not \(\tan x\). Exam tip: Remember \(\tan x\) as \(\sin x/\cos x\).
View question details\(\tan x=\frac{\sin x}{\cos x}\). It is undefined when \(\cos x=0\), i.e. at \(x=\frac{(2n+1)\pi}{2}\). At \(x=n\pi\), tan equals 0, so option A is not correct. Exam tip: link tan’s domain to non-zero cosine.
View question details(\cosec x=\frac{1}{\sin x}). Hence (\sin x=\frac{1}{4}); learn each reciprocal function as a pair.
View question detailsUsing the Pythagorean identity \(\sin^2 x+\cos^2 x=1\), we get \(1-\cos^2 x=\sin^2 x\). Therefore, \(\frac{1-\cos^2 x}{\sin^2 x}=\frac{\sin^2 x}{\sin^2 x}=1\), provided \(\sin x\ne 0\). Neither \(\sin x\), \(\cos x\), nor \(\tan x\) is the simplified value of this ratio. Exam tip: first replace \(1-\cos^2 x\) with \(\sin^2 x\) in such questions.
View question detailsSince (1-\sin^2 x=\cos^2 x), the value is (1). (\sin^2 x+\cos^2 x=1) is the most important identity.
View question detailsThe period of (\sin kx) is \(\frac{2\pi}{k}\). Here \(k=3\), so the period is \(\frac{2\pi}{3}\).
View question detailsThe period of (\tan kx) is \(\frac{\pi}{k}\). Substituting \(k=4\) gives period \(\frac{\pi}{4}\).
View question detailsSince \(\cos x\) lies between \(-1\) and \(1\), multiplying by 2 gives values of \(2\cos x\) from \(-2\) to \(2\). The endpoints are included because \(2\cos 0=2\) and \(2\cos \pi=-2\). Thus, \([-1,1]\) is the range of \(\cos x\), not of \(2\cos x\). Exam tip: the range of \(a\cos x\) is \([-|a|,|a|]\).
View question detailsSince \(\sin x\) lies between \(-1\) and \(1\), its maximum value is \(1\). Therefore, the maximum of \(3\sin x+1\) is \(3\times1+1=4\). Option 3 is only the maximum of \(3\sin x\); adding the constant \(1\) shifts the maximum to 4. Exam tip: for \(a\sin x+b\), when \(a>0\), the maximum value is \(a+b\).
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