Ранжируем ряд:
2,<span>3,</span><span>3,</span><span>3, </span><span>6,</span><span>7,</span><span>7,</span><span>9</span>
Мода = 3
<span>1)81с^2-d^2 + 9c + d=(9c-d)(9c+d)+(9c+d)=(9c+d)(9c-d+1)
2)25x^2 - 10xy +y^2 -9=(5x-y)^2-9=(5x-y-3)(5x-y+3)</span>