Question

solve with steps please

Answer 1

HELLO DEAR,

k = sin(180/18) . sin(5×180/18) . sin(7×180/18)

=> sin10 × sin50 × sin 70

=> cos80 × cos40 × cos20


$\frac{1}{2sin20} (2sin20cos20)(cos40cos80) \\ \\ = > \frac{1}{2sin20} sin(2 \times 20)cos40cos80 \\ \\ = > \frac{1}{4sin20}(2 \times sin40cos40)cos80 \\ \\ = > \frac{1}{4sin20} (sin2 \times 40)cos80 \\ \\ = > \frac{1}{8sin20} (2sin80 \times cos80) \\ \\ = > \frac{1}{8sin20} (sin160) \\ \\ = > \frac{1}{8sin20} (sin180 - 20) \\ \\ = > \frac{1}{8sin20} sin20 \\ \\ = > \frac{1}{8}$


hence, option (c) is correct


I HOPE ITS HELP YOU DEAR,
THANKS

Answer 2

Hi,

Please see the attached file!


Thanks