1/(√2 + √5 + √7) = (√2 + √5 - √7)/[(√2+√5)² - 7] = (√2 + √5 - √7)/(2√10) =
= (√20+√50-√70)/20 = (2√5 + 5√2 - √70)/20
1/(√2 + √5 + √7) = (√2 + √5 - √7)/[(√2+√5)² - 7] = (√2 + √5 - √7)/(2√10) =
= (√20+√50-√70)/20 = (2√5 + 5√2 - √70)/20