Verified answer

1)  7m (m³-8m+9) = 7m⁴ - 56m³ + 63

   ( x-2 )( 2x+3 ) = 2x²- 4x - 6

   ( 3m - 4n)( 5m + 8n) = 15m² + 24mn- 20mn - 32n² = 15m² + 4mn - 32n²

   ( y+3 )( y² + y - 6 )= y³ + y² - 6y +3y² + 3y - 18 = y³+4y² - 3y - 18

2)  12ab - 18b² =  6b (2a - 3b )

    21x⁷ - 7x⁴ = 7x⁴ ( 3x³ - 1 )

    8x - 8y + ax - ay = 8 ( x-y ) +a ( x-y ) = ( x-y )( 8+a )

3)   2c ( 3c - 7 ) - ( c - 1 )( c + 4 ) = 6c² - 14c - ( c² + 4c - 4 ) = 5c² - 18c + 4

4)   y = -0,6   ,   14xy - 2y + 7x - 1 = -8,4x + 1,2 + 7x - 1 = -1,4x + 0,2