exam Maths Puzzle Numerical Ability

Identity:
tan(45+a)-tan(45-a)

tan45+tana/1-tan45tana - tan45-tan+tana/1+tan45tana
=tan45+tana-tan45+tana/1-tan45tana+tan45tana
=2tana/1-tana
What am I doing wrong?

possi

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exam Other Question

explain why a polynomial function of even degree cannot have an inverse.
Does anyone know how to do this problem?

I need to find the constant of variation k

M varies directly with N; M = 144 when N= 8

Thanks,
sher