Question

(1+cot78)(1+cot57) = find answer​

Answer 1

cot(78)=tan12

               cot(57)=tan33

(1+tan12)(1+tan33

=1+tan12+tan33+tan12.tan33

Now,                            ----------(1)

45=12+33

tan45 tan(12+33)

1=tan12+tan33

___________________

1-tan12.tan33

∴

1-tan12.tan33=tan12+tan33

∴

1=tan12.tan33+tan12+tan33

Thus, substituting above result in eq(1)

=1+1

=2

Refer the image..