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( x^2 + a )^2 - ( bx + 7 )^2

where a,b are constant. find the values of a and b. hence, or otherwise, factorise f(x) completely.

the value of a and b are -13 and 1 respectively.

so,

f(x) = ( x^2 - 13 )^2 - ( x + 7 )^2

one way to factorise f(x) completely is to substitute value of x so that we can get

f(x) = 0.

is there any other easier way since there is a keyword "HENCE" in the question.

thank you.