Q. 9. 
term of an A.P 
= a + (n-1 ) d
Q.10.um of n terms of an A.P :
(or)
Q.11. Two triangles are said to be similar , if
(i) All the corresponding angles are equal
(ii) All the corresponding sides are proportional.
Q.12.Basic proportionality theorem (Thales theorem ). In a triangle , if a line is drawn parallel to one side of a triangle it divides the other two sides in the same ratio,
i.e., if in 
ABC , DE|| BC , then 
= 
Q.13.CONVERSE OF BASIC PROPORTIONALITY THEOREM : In a triangle , if a line divides the two sides in the same ratio , then line is parallel to the third side .
i. e ., in ABC , if DE is a line such that = = , then DE|| BC
Q. 14. If two triangles are similar , then the ratio of their areas is equal to the ratio of the squares of their corresponding sides .i.e., if ABC 
DEF Then
=
= 
= 
Q. 15. PYTHAGORAS THEOREM :In a right angled triangle , the square of the hypotenuse is equal to sum of the squares of the other two sides .
Q. 16. CONVERSE OF THE PYTHAGORAS THEOREM : In a triangle , if square of one side is equal to the sum of the squares of the other two sides , then triangle is right angled .
Q. 17. DISTANCE FORMULA : Distance between two points , A ( 
,
) and B( 
, 
) is given by
AB =
