The last bus has gone. Can you___walk___ home?

I. Simple past or present perfect

1. I first (read) read it in 2005. (simple past)

2. I (complete) have completed my paper at last. (present perfect)

3. The day before yesterday, we (have) had a bad storm. (simple past)

4. I (never be) have never been to Italy. (present perfect)

a) Ta có: A = x² + 10x + 46

= x² + 5x + 5x + 25 + 21

= x (x + 5) + 5 (x + 5) + 21

= (x + 5)(x + 5) + 21

= (x + 5)² + 21

Ta có: (x + 5)² \(\ge\) 0 \(\forall\) x

21 > 0

\(\Rightarrow\) (x + 5)² + 21 > 0 \(\forall\) x

Vậy đa thức A không có nghiệm.

b) Ta có: B = x⁴ + 3x² + 1

= x⁴ + 2x² + 1 + x²

= (x² + 1)² + x²

Ta có: (x² + 1)² > 0 \(\forall\) x

x² \(\ge\) 0 \(\forall\) x

\(\Rightarrow\) (x² + 1)² + x² > 0 \(\forall\) x

Vậy đa thức B không có nghiệm.

Ta có: \(1^x=1\forall x\in R\)

\(\Rightarrow5^{\left(x-2\right)\left(x+3\right)}=1\forall x\in R\)

\(\Rightarrow\left(x-2\right)\left(x+3\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-2=0\\x+3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=-3\end{matrix}\right.\)

Vậy x = 2 hoặc x = -3

nhầm nữa: III.2 là The man who is my teacher is tall :v