What is the portion of the quadratic formula under the square root sign

Will mark brainliest question in the pic.

Find the equation of the line that goes through the points (4, –1) and (2, –5). use slope formula, equation, to find the slope of a line that passes through the points. m = use slope-intercept form, y = mx + b, to find the y-intercept (b) of the line. b = write the equation in slope-intercept form, y = mx + b.

Find the value of x that will make l ll m