Question

http://prntscr.com/b5gmq8

Answer 1

Perhaps easier to start with something non algebraic

What is the LCD of say

\[\frac{ 1 }{ 5 } + \frac{ 1 }{ }\]

Answer 2

should say 1/5 + 1/3

Answer 3

Its either that or d

Answer 4

for 1/5 and 1/3 the LCD is 15 (5 x 3)
For 1/9 and 1/3 the LCD is 9 (since firstmultiples of 3 and 9 are common at 9)

basically LCD is finding the lowest common multiple of the two denominators.
So you expect your answer to contain at least everything from each denominator.

The denominators are
\[x^2y; xy^2\]
So your answer needs to have at least an x^2 and at least a y^2, the largest bits of both!

Answer 5

it cannot be b because the first denominator x^2y has x^2, which is larger than x to start with. Lowest common denominator must be equal to or larger than starting power of x.

Answer 6

Oh okay so it will be d

Answer 7

yup. just think of needing to 'cover' what is already there

Answer 8

Thank you