Question

calculând (sin 30°+cos30°)•(cos 60°- sin 60°)​

Answer 1

$sin \ 30\textdegree = \frac{1}{2}$

$cos \ 30\textdegree = \frac{\sqrt{3} }{2}$

$cos \ 60\textdegree = \frac{1}{2}$

$sin \ 60\textdegree = \frac{\sqrt{3} }{2}$

$(\frac{1}{2} + \frac{\sqrt{3} }{2} ) \cdot (\frac{1}{2} - \frac{\sqrt{3} }{2} )=$

$\frac{1+\sqrt{3}}{2}\cdot \frac{1-\sqrt{3}}{2} =$

$\frac{\left(1+\sqrt{3}\right)\left(1-\sqrt{3}\right)}{2\cdot \:2} =$

$\frac{-2}{2\cdot \:2} =-\frac{1}{2}$