CBSE Guess > Papers > Question Papers > Class X > 2009 > Mathematics > Mathematics

Q. 19. Find the sum of all three digit numbers which are divisible by 7.

Sol. To find : 105 + 112 + 119 + … + 994
Ist term, a = 105
Common difference, d = 112 – 105 = 7
an = 994
a + (n – 1)d = 994
105 + (n – 1)7 = 994
(n – 1)7 = 994 – 105 = 889

Q. 20. Prove that :

Sol. See Q. 20, 2008(I OD).

Or

Using Geometry, find the value of sin 60°.

Sol.

Δ ABC be an equilateral, Let each side be 2a. Since each angle in equilateral Δ is 60°

Mathematics 2009 Question Papers Class X
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