Question

Exercitiile 1 si 2. ................

Answer 1

1.a..A+B+C=180
90+B+C=180
B+C=90
B=90-C
B-C=90-C-C=90-2C
cos(B-C)=cos(90-2C)=sin 2C=2sinC*cosC=2*c/a*b/a=1bc/a^2

b..tg2C=2tgC/((1-tg^2 C)=2*c/b)/(1-c^2/b^2)
2c/b*b^2 /(b^2-c^2)=2bc/(b^2-c^2)

c....ctgB+1/sinB=c/b+a/b=(c+a)/b