For five individuals the blood platelet aggregation was measured before (x1) and after (y1) they performed a certain task. these five pairs of values gave the following results: ¯x1 = 30.2, y¯1 = 39.0, cov(x1, y1) = 88.5. for another six individuals the blood platelet aggregation was also measured before (x2) and after (y2) they performed the same task. these six pairs of values gave the following results: ¯x2 = 52.17, y¯2 = 63.67, cov(x2, y2) = 148.67. find the covariance of the combined 11 pairs.

Intersecting secant-tangent theorem states that if a tangent segment and a secant segment are drawn to a circle from an exterior point, then the square of the measure of the tangent segment is equal to the product of the measures of the secant segment and its external secant segment.so to break it down: 1. pq acts as the tangent and ps as the secant with an intersection at p.sr = 21rp = 3x + 3pq = 4x + 4following to equation: tangent squared = the two segments multiplied by each otherso (4x + 4) ^ 2 = (3x + 3) • (21) simplifies to 16x^2 - 31x - 47 = 0 or (16x - 47)(x + 1) x = -1 or x = 47/162. pq acts as the tangent and ps as the secant with an intersection at p (again! )sr = 16rp = xpq = 15(15) ^ 2 = 16 • x225 = 16xx = 225/163. the interesting chords are proportional to each other so a ratio is possible to set up: ap dp 10 3 + x = = —— = pc pb 8 xcross multiple to get 10x = (3 + x)(8)x = 12