1.

Write the value of \(\begin{vmatrix}sin\,20° & -cos\,20° \\[0.3em]sin\,70°& cos\,70° \\[0.3em]\end{vmatrix}\).

Answer»

\(\begin{vmatrix}sin\,20° & -cos\,20° \\[0.3em]sin\,70°& cos\,70° \\[0.3em]\end{vmatrix}\)

= sin 20° . cos 70° + cos 20° . sin 70°

= sin (20° + 70°)

= sin 90°

= 1.



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