Question
If 6x - 3y = 9, and 9xy = 18, then what is the value of 6x
+ 3y?Solution
ATQ,
Given: 6x - 3y = 9
And 9xy = 18
Or, xy = 2
We know that, (a + b)² = a² + b² + 2ab
And (a - b)² = a² + b² - 2ab
Or, (a + b)² - (a - b)² = 4ab
So, (6x + 3y)² - (6x - 3y)² = 4 × 6x × 3y
Or, (6x + 3y)² - 9² = 144
Or, (6x + 3y)² = 225
So, 6x + 3y = ±15
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