Remember This!

These are the formulae used in solving algebraic problems. So, 'gune sokmo deh'!

We use Formula (1) to solve quadratic equation. You can find the roots of a quadratic equation with this formula. There are also another methods to find the roots of a quadratic equation;

 i) by factorisation, and ii) by completing the square.

Formula (2) , (3)  and (4) are laws of indices.

Formula (5) , (6) , (7) , (8) are laws of logarithms.

Formula (9) and (10) are formulae for arithmetic progressions (A.P). 

Formula (9) : to find the nth term of an A.P

Formula (10) : to find the sum of the first nth terms of an A.P 

Formula (11) , (12) , and (13) are formulae for geometric progressions (G.P)

Formula (11) : to find the nth term of a G.P

Formula (12) : to find the sum of the first nth terms of a G.P. To use it depends on the value of 'r'. 

If  r >1 , use the formula on your left,

If r <1 , the the formula on your right

Formula (13) : to find the sum to infinity of a G.P

You can distinguish the formula for A.P and the formula for G.P by looking at the 'd' and 'r' in each of these formulae. 

• If you see 'd', then it is for A.P because d = common difference, and a common difference is the characteristics of an A.P. 
• When you see 'r' in the formula, then use it for G.P because r = common ratio, which is the characteristic of a G.P.