OG详解-OG8 数学1 Q14

The correct answer is 6. Applying the distributive property to the expression ry⁴ (15y-9) yields 15ry⁵ -9ry⁴. Since 90y⁵ -54y⁴  is equivalent to ry⁴ (15y-9), it follows that 90y⁵ -54y⁴  is also equivalent to 15ry⁵ -9ry⁴ . Since these expressions are equivalent, it follows that corresponding coefficients are equivalent. Therefore, 90 = 15r and -54=-9r. Solving either of these equations for r will yield the value of r. Dividing both sides of 90 = 15r by 15 yields 6 = r. Therefore, the value of r is 6.