book Maths Puzzle Numerical Ability

ok i need to know what does all them letters mean cause i don't get it

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book Other Question

4x(squared) - 17x + 4 = 0

Solved by completing the square. Not sure what to do with the coefficient 4 Find the equaton of the line through the points (-3,1)&(5,-5). Write your solution in each of the three forms.