I would like to confirm my answers for these questions before carrying out with more studying--since there are no answers, and I'm worried I will be practicing incorrectly.
Let F(x)="x is friendly", T(x)="x is tall" and A(x)="x is angry" note: ~ = negation
Ex 1. Some people are not angry
My answer: ∃x~A(x)
Ex 2. All tall people are friendly
My answer: ∀xT(x) -> F(x)
Ex 3. No friendly people are angry
My answer: ∀xF(x) -> ~ A(x)
I'm feel confident the answers are correct, but just in case.
In the second and third answers the quantifier is intended to apply to the entire expression that follows it, which therefore needs to be in parentheses: $$\forall x\big(T(x)\to F(x)\big)$$ and $$\forall x\big(F(x)\to\neg A(x)\big)\;.$$ $\forall xT(x)\to F(x)$ without the extra parentheses means $\big(\forall T(x)\big)\to F(x)$, which doesn’t actually say anything, since the $x$ in $F(x)$ is a so-called free variable: it’s an unquantified placeholder. The closest you can come to an English translation is If everyone is tall, then x is friendly, but $x$ doesn’t actually refer to anyone in particular.
In other words, quantifiers behave rather like the negative sign in arithmetic and algebra: if you want the negative of $a+b$, you need to use parentheses and write $-(a+b)$, because $-a+b$ means $(-a)+b$.
Because of the negation I prefer to use the extra parentheses even in your first expression, writing $\exists x\big(\neg A(x)\big)$, but some people are comfortable with your version.