Answer:
vertex is (9,-21)
Explanation:
we are given function as
![f(x)=x^2-18x+60](https://img.qammunity.org/2020/formulas/mathematics/middle-school/jrnbc8ary0whbuw7vl0fkt47xl61edskgn.png)
we can use vertex form of parabola
![f(x)=a(x-h)^2+k](https://img.qammunity.org/2020/formulas/mathematics/high-school/7ipmrrobocsxyi038fh5rmhmhaf4i7cji9.png)
So, firstly we will complete x square
![f(x)=x^2-2* x* 9+60](https://img.qammunity.org/2020/formulas/mathematics/middle-school/kcakw3u6mrhto18q7imswfok7i5khmjtdm.png)
we can sue formula of square
![a^2+2ab+b^2 =(a+b)^2](https://img.qammunity.org/2020/formulas/mathematics/middle-school/cj0lxh42f0cq0nf1cnpng2vy3dli0vstnn.png)
![f(x)=x^2-2* x* 9+60](https://img.qammunity.org/2020/formulas/mathematics/middle-school/kcakw3u6mrhto18q7imswfok7i5khmjtdm.png)
so, we will add and subtract 9^2
![f(x)=x^2-2* x* 9+9^2+60-9^2](https://img.qammunity.org/2020/formulas/mathematics/middle-school/5exorqfrzi3dtwzadyn4t30i4mwam6fj3s.png)
![f(x)=(x-9)^2+60-9^2](https://img.qammunity.org/2020/formulas/mathematics/middle-school/ybeltm8159eb8clh50tw65iqdan4cyodhw.png)
![f(x)=(x-9)^2-21](https://img.qammunity.org/2020/formulas/mathematics/middle-school/npvhiiikho2mc9rdllhwyg3mnd8wt4nbgh.png)
now, we can compare it with vertex form of formula
![f(x)=a(x-h)^2+k](https://img.qammunity.org/2020/formulas/mathematics/high-school/7ipmrrobocsxyi038fh5rmhmhaf4i7cji9.png)
so, we get
![h=9,k=-21](https://img.qammunity.org/2020/formulas/mathematics/middle-school/camyya0jxnt2nux1e9qzhxg8r2jrvbrokq.png)
So, vertex is (9,-21)