We have,
tan−112+tan−113
We know that,
tan−1x+tan−1y=tan−1(x+y1−xy)
So,
tan−112+tan−113=tan−1⎛⎜ ⎜ ⎜⎝12+131−12×13⎞⎟ ⎟ ⎟⎠
=tan−1⎛⎜ ⎜ ⎜⎝3+261−16⎞⎟ ⎟ ⎟⎠
=tan−1(55)
=tan−11
=tan−1tanπ4
=π4