- Home
- Standard 11
- Mathematics
Trigonometrical Equations
normal
જો $\cos \theta = \frac{{ - 1}}{2}$ અને ${0^o} < \theta < {360^o}$ તો $\theta $ ની કિમતો મેળવો.
A
${120^o}$ અને ${300^o}$
B
${60^o}$ અને ${120^o}$
C
${120^o}$ અને ${240^o}$
D
${60^o}$ અને ${240^o}$
Solution
(c) Given, $\cos \theta = \frac{{ – 1}}{2}$ and ${0^o} < \theta < {360^o}$.
We know that $\cos {60^o} = \frac{1}{2}$ and $\cos ({180^o} – {60^o})$ $ = – \cos {60^o} = – \frac{1}{2}$ or $\cos {120^o} = – \frac{1}{2}$.
Similarly $\cos ({180^o} + {60^o})$ $ = – \cos {60^o} = – \frac{1}{2}$
or $\cos {240^o} = – \frac{1}{2}.$
Therefore $\theta = {120^o}$ and ${240^o}$.
Standard 11
Mathematics
