exam Maths Puzzle Numerical Ability

How do I solve 10x4 - 30x3 - 50x - 20 ? (Please note 4 and 3 are exponents.)

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exam Other Question

a a+b
- + ---
b a-b
_______
a a-b
- - ---
b a+b
In other terms:
[(a/b)+(a+b)/(a/b)]/[(a/b)-(a-b)/(a+b)]

I tried to multiply both denominator and numerator by [b(a+b)(a-b)}] but that didnt seem to work for me. show that median devides a triangle in two equal parts?