RRB NTPC Mains or Stage 2 Model Paper 5 with solutions

Question : 11 of 120

Marks: +1, -0

In a right angled △ABC,∠C = 90º and CD is perpendicular to AB. If AB × CD = CA × CB, then

1 /{CD^2}

is equal to

Solution:

In ΔABC
CD ⊥ AB
and AB × CD = CA × CB ... (i)
In ΔCDB

BC^2 = BD^2 + CD^2

... (ii)

CD^2 = BC^2 – BD^2

From eq. (i) and (ii)

1 /{CD^2} =1/{BC^2} -1/{CA^2}

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