Fill in the blank $(x+a)(x+b)=x^2$+______ $x+a b$

To do: Fill in the blanks

Solution:

$(x + a) (x + b)$  

Multiply each and every term inside the brackets,

$x \times x  =  x^2$   

$x \times a  =  a x$

$x \times b  =  b x$

$a \times b  =  a b$

add all,

$x ^2   +  a x  +  b x  +  ab$

$ x^2 +  (a+b)x  + ab$                         [$ax + bx = [a+b]x$  ;  take $x$ as common]

$(x + a) (x + b)   =   x^2  +  (a+b)x  + ab$   

So, $(a+b)$ will be filled in the bank.