Question

if (a+b)^2=361 and ab=-120, calculate the value of a^2+b^2

Answer 1

It's Pretty simple,

We know that (a+b)² = a² + b² +2ab ,

Now, Subtracting 2ab on both sides,

=> (a+b)² - 2ab = a² + b² , Now we can find the answer quickly,

Given that, 
(a+b)² = 361 and ab = -120, 
=> 2ab = 2 * -120 = -240,

Now inputting the values in the above formula,

=> 361 + 240 = a² + b²,
=> a² + b² = 601,

Hope you understand, Have a great day !

Answer 2

(a+b)^2=361
a^2+b^2+2ab=361
a^2+b^2+2(-120)=361. {given ab=-120}
a^2+b^2-240=361
a^2+b^2=361+240
a^2+b^2=601