А) 2sin^x-5sinx-3=0

б) 2tg+2ctg=5

2sin²x-5sinx-3=0

sinx=a

2a²-5a-3=0

D=25+24=49

a1 = (5-7) / 4=-1/2⇒sinx=-1/2⇒x = (-1) ^ (n+1) * π/6+πn, n∈z

a2 = (5+7) / 4=3⇒sinx=3>1 нет решения

2tgx+2ctgx=5

2tgx+2/tgx-5=0

2tg²x-5tgx+2=0, tgx≠0

tgx=a

2a²-5a+2=0

D=25-16=9

a1 = (5-3) / 4=0,5⇒tgx=0,5⇒x=arctg0,5+πn, n∈z

a2 = (5+3) / 4=2⇒tgx=2⇒x=arctg2+πk, k∈z