设实数ab满足3a²-10ab+8b²+5a-10b=0,求u=9a²+72b+2的最小值

设实数ab满足3a²-10ab+8b²+5a-10b=0,求u=9a²+72b+2的最小值
设实数ab满足3a²-10ab+8b²+5a-10b=0,求u=9a²+72b+2的最小值

设实数ab满足3a²-10ab+8b²+5a-10b=0,求u=9a²+72b+2的最小值
(a-2b)(3a-4b)+5a-10b=0
(a-2b)(3a-4b+5）=0U=9a^2+72b+2中将a=2b或4b=3a+5带入
则当a=2b时,u=-34
当4b=3a+5时,u=11
取最小值,所以u=-34