Mathematical statement with two expression that have the same value.
x + 2 = 3
j-7=4 1+1=2 b=4 3a-2=a+2 4=4

c=4

Writing expression- An expression can be written using a single construct, a single variable a combination of operation with construct variable, or numeral coefficient.
2 y-7 4+3=7 1c+3=7 3c-5 2c+4=10 3x+2=11
Sorry would not work here is the link.
http://www.youtube.com/watch?v=G6fPIVeS_-A