The sum of two numbers a and b is 20. Write an expression for the sum of their squares, in terms of a.
I used your tip and im stuck. I got:
So when it asks "Write an expression for the sum of their squares, in terms of a." I wrote b=20-a and 10=20-10 but the answer still is wrong. Do you know where i was wrong?
a^2+b^2 would be 10^2+10^2 which is 100+100 and the answer is 200. Its wrong.
a and b are unknown.
you keep saying a=10 and b=10 but that is only one of an infinite number of possibilities.
a could be 8 and b 12
or a could be 5.3 and b could be 14.7
or a could be pi and b could be 20-pi
What you know is that a+b=20 which means b=20-a
You want the sum of their squares is a^2 +b^2 but we have to replace b with 20-a
\(a^2+b^2\\ =a^2+(20-a)^2\\ =a^2+400+a^2-40a\\ =2a^2-40a+400\)