JAMB - Mathematics (1978 - No. 40)
Evaluate without using tables sin(-1290º)
\(\frac{3}{2}\)
-\(\frac{3}{2}\)
\(\frac{2}{2}\)
1
\(\frac{1}{2}\)
Giải thích
sin(-1290º) = -sin(1290º)
sin([3*360] + 210)
where sin 360 = 0 and sin 210 = 180 + 30 ⇔ -30º
-sin ([3* 0] + [-30])
-sin(-30)
sin30 = \(\frac{1}{2}\)