Question

№1 и №3 помогите пожалуйста

Answer 1

№1
$0,04 leq 5^{2-x} leq 25 \ 5^{-2} leq 5^{2-x} leq 5^2 \ -2 leq 2-x leq 2 \ -4 leq -x leq 0 \ 0 leq x leq 4 \ OTBET:0; 1; 2; 3; 4.$
№3
$frac{sina}{1+cosa} + frac{1+cosa}{sina} = frac{2}{sina} \ frac{sin^2a+(1+cosa)^2}{sina(1+cosa)} = frac{2}{sina} \ frac{sin^2a+1+2cosa+cos^2a}{sina(1+cosa)}= frac{2}{sina} \ frac{2+2cosa}{sina(1+cosa)}= frac{2}{sina} \ frac{2(1+cosa)}{sina(1+cosa)} = frac{2}{sina} \ frac{2}{sina} = frac{2}{sina}$