Twenty one times of a positive number is less than its square by 100. The value of the positive number is

The value of 

(cosec a - sin a) (sec a-cod a) (tan a + cot a)

If 7 sin²θ+3cos²θ=4, then the value of tan θ is (θ is acute)

If a + b = 1, find the value of a³+b³-ab-(a²-b²)²

Articles are marked at a price which gives a profit of 25%. After allowing a certain discount the profit reduces to 12 1/2%. The discount percent is

In Δ ABC, ∠ BAC = 900 and AD ⊥ BC. If BD = 3 cm and CD = 4 cm, then the length (in cm) of AD is