6. Diketahui \( \cos (a+b)=\frac{1}{2} \) dan \( \cos (a-b)=\frac{1}{8} \operatorname{Nilai}(\sin a+\sin b)=\cdots \) \( \begin{array}{ll}\text { a. }-\frac{5}{3} & \text { d. } \frac{5}{16} \\ \text { b. }-\frac{3}{5} & \text { e. } \frac{5}{3} \\ \text { c. } \frac{3}{16} & \end{array} \)

1. COMPRENDE. Representa en un plano cartesiano dos ángu los que sean coterminales al ángulo dado en cada punto. a. \( -\frac{\pi}{4} \) b. \( \frac{3 \pi}{2} \)

\( A B C \) is a triangle. \( A C K K .9 \mathrm{~cm} \) Angle \( B=90^{\circ} \) Angle \( C=38^{\circ} \) Calculate the length of \( B C \). Give your answer correct to 3 significant figures.

a) \( \cos ^{2} x-3 \operatorname{sen}^{2} x=0 \) b) \( \cos 2 x=1+4 \operatorname{sen} x \)

Triangle \( P Q R \) has a right angle at \( Q \). \( P Q=3.4 \mathrm{~cm} \) and \( P R=5.8 \mathrm{~cm} \). Work out the size of angle \( Q R P \). Give your answer correct to 1 decimal place.

\( g ( x ) = \cos ( x ) - \sin ( x ) = 0 \)