Question

sina cosB-sin(a-B)​
cos a cos B - cos(a-B)
1-tgx / 1+tgx

Answer 1

Объяснение:

$sin alpha cos beta - sin( alpha - beta ) = sin alpha cos beta - sin alpha cos beta + cos alpha sin beta = cos alpha sin beta .$

$os alpha cos beta - cos( alpha - beta ) = cos alpha cos beta - cos alpha os beta - sin alpha sin beta = - sin alpha sin beta$

$frac{1 - tgx}{1 + tgx} = frac{1 - frac{sinx}{cosx} }{1 + frac{sinx}{cosx} } = frac{cosx - sinx}{cosx + sinx} = frac{sin( frac{pi}{2} - x) - sinx}{sin( frac{pi}{2} - x) + sinx } = frac{2sin( frac{pi}{4} - x)cos frac{pi}{4} }{2sin frac{pi}{4}cos( frac{pi}{4} - x) } = tg( frac{pi}{4} - x)$