I think of a two digit number.The sum of the digits is 9.
When the number is reversed and subtracted from the
original, the result is 45. Find the original number
There are 5 more girls than boys in a class. If 2 boys join
the class, the ratio of girls to boys will be 5:4. Find the
number of of girls in the class.
In finding the equations of the
bisectors of the angles between two
lines a_1 x+b_1 y+c_1 =0 and a_2 x+b_2 y+c_2 =0,
why we observe a_1 a_2 +b_1 b_2 >0 or <0
for obtuse and acute angle bisectors?