How to fix failed to resolve :com.android.support :appcompat-v7:27.+'-error

Easy way to fix
just open your android project

open build.gradle(Master file)
and add this line to
if your android version is less than 3

repositories {
jcenter()
mavenLocal()
mavenCentral()
maven { // <-- Add this
url 'https://maven.google.com/'
name 'Google'
}
}

if your android version is greater than 3
than
repositories {
jcenter()
mavenLocal()
mavenCentral()
google() //---> Add this
}

Also add in allproject file

allprojects {
repositories {
jcenter()
mavenLocal()
mavenCentral()
google()
}
}

Now open your build.gradle file in app

and add this implementation
dependencies {
implementation 'com.android.support:appcompat-v7:27.+'
implementation "com.android.support:support-core-utils:27.1.1"
}