header on first page and others

Question

a header is created for pages 2+ with fancyhdr but how can you make the same header also appear on the first page?

here is the rmarkdown:

---
title: "Untitled"
classoption: landscape
output: 
  pdf_document:
    number_sections: false
    dev: pdf
    keep_tex: false
    toc: yes
header-includes:
- \usepackage{fancyhdr}
- \pagestyle{fancy}
- \fancyhead[C]{center text}
- \fancyhead[R]{right text}
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```

## R Markdown

This is an R Markdown document. Markdown is a simple formatting syntax for authoring HTML, PDF, and MS Word documents. For more details on using R Markdown see <http://rmarkdown.rstudio.com>.

When you click the **Knit** button a document will be generated that includes both content as well as the output of any embedded R code chunks within the document. You can embed an R code chunk like this:

```{r cars}
summary(cars)
```

## Including Plots

You can also embed plots, for example:

```{r pressure, echo=FALSE}
plot(pressure)
```

Note that the `echo = FALSE` parameter was added to the code chunk to prevent printing of the R code that generated the plot.

Answer 1

Include \thispagestyle{fancy} in the beginning of your document (e.g. just after the yaml header) to make the first page fancy.

Edit to address your comment

If you want to have different center text in the first page you can have use if when you define \fancyhead

\fancyhead[C]{\ifnum\value{page}>1 center text \else \fi}