Solution 2.1:1f
From Förberedande kurs i matematik 1
The squaring rule \displaystyle (a+b)^2 = a^2+2ab+b^2 with \displaystyle a=5 and \displaystyle b=4y gives
| \displaystyle \begin{align}
(5+4y)^2 &= 5^2+ 2\cdot 5 \cdot 4y +(4y)^2 \\[3pt] &= 25+10\cdot 4y + 4^2y^2\\[3pt] &= 25+40y+16y^2\\[3pt] &= 16y^2 +40y + 25\,\textrm{.} \end{align} |
