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Introduction To Trigonometry

Question
CBSEENMA10006987

Find the values of y for which the distance between the points P(2, – 3) and Q(10, y) is 10 units.

Solution

We have, P(2, -3), Q( 10, y) and PQ = 10 units.
Now,    PQ2 = (10)2 = 100
⇒ (10 - 2)2 + {y - (-3)}2 = 100
⇒    (8)2 + (y + 3)2 = 100
⇒    64 + y2 + 6y + 9 = 100
⇒    y2 + 6y - 21 = 0
⇒    y2 + 9y - 3y - 27 = 0
⇒    y(y + 9) - 3(y + 9) = 0
⇒    (y + 9) (y - 3) = 0
⇒    y + 9 = 0
or    y - 3 = 0
⇒    y = -9
or    y = 3
⇒    y = -9, 3
Hence, the required value of is -9 or 3.