Final answer:
To find the value of 1/a, substitute the given expression for a into the expression 1/a. Simplify the resulting expression by finding a common denominator, combining the fractions, and simplifying further. The final value of 1/a is xy/(y + x).
Step-by-step explanation:
To find the value of 1/a, we need to substitute the given expression for a into the expression 1/a. So if a = 1/x + 1/y, then 1/a can be written as:
1/a = 1/(1/x + 1/y)
To simplify this expression, we need to find a common denominator for 1/x and 1/y. The common denominator is xy. So we rewrite 1/x and 1/y with the common denominator:
1/x = y/xy
1/y = x/xy
Now we can substitute these values back into the expression for 1/a:
1/a = 1/(y/xy + x/xy)
Next, we can combine the fractions by adding the numerators:
1/a = 1/((y + x)/xy)
We can simplify this further by multiplying the numerator and denominator by xy:
1/a = xy/(y + x)
Therefore, the value of 1/a is xy/(y + x).