First exercise:
Let's call the initial weight of the dog [tex] w_0 [/tex]. We know that after the first year the difference is -1.56 pound, so the weight after one year is [tex] w_1 = w_0-1.56 [/tex]
After another year, the new weight is [tex] w_2 = w_1 + 0.73 [/tex] But we know the way to express [tex] w_1 [/tex] in terms of [tex] w_0 [/tex], so we have
[tex] w_2 = w_1 + 0.73 = (w_0-1.56)+0.73 = w_0 + (-1.56+0.73) = w_0 - 0.83[/tex]
Second exercise:
You need an equation to be satisfied when [tex]x = 26 [/tex]. Actually, this is already an equation, so we can simply rearrange it to get [tex] x-26 = 0 [/tex], which is an equation with solution 26.
Third exercise:
Rearrange the left hand side to get
[tex] -0.01 + 8 = x - 0.3 + 8 [/tex]
Since 8 appears in both sides, we can simplify it:
[tex] -0.01 = x - 0.3 [/tex]
Add 0.3 to both sides:
[tex] 0.29 = x [/tex]
