A-level Maths · Coordinate geometry

Centre and radius of a circle

Complete the square in x and y to find the centre and the radius of a circle.

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Question 1

A circle has equation x2+y2+8x−4y−30=0x^{2} + y^{2} + 8x - 4y - 30 = 0. Find the coordinates of the centre of the circle and the radius of the circle. Give the radius in exact form.

Your answer

Fill in every box. Give numbers like 4.53 or -0.2, or a fraction such as 7/3. Where an exact answer is asked for, use roots, ln and π with no decimals: for example 2√3 or 3π/4.

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