fixed 96a21d71 from https://gitee.com/esterzhou/docs/pulls/16639

Update doc (16412)
Signed-off-by: Nester.zhou <ester.zhou@huawei.com>

en/application-dev/faqs/faqs-device-management.md

@@ -2,23 +2,21 @@
 
 ## How do I obtain the DPI of a device?
 
-Applicable to: OpenHarmony SDK 3.2.2.5, stage model of API version 9
-
-Import the **\@ohos.display** module and call the **getDefaultDisplay** API.
+Applicable to: OpenHarmony 3.2 Beta5, stage model of API version 9
 
-Example:
+Import the **@ohos.display** module and call the **getDefaultDisplaySync** API.
 
+**Example**
 
 ```
 import display from '@ohos.display'; 
-display.getDefaultDisplay((err, data) => { 
-  if (err.code) { 
-    console.error('Test Failed to obtain the default display object. Code: ' + JSON.stringify(err)); 
-    return; 
-  } 
-  console.info('Test Succeeded in obtaining the default display object. Data:' + JSON.stringify(data)); 
+let displayClass = null;
+try {
+    displayClass = display.getDefaultDisplaySync();
  console.info('Test densityDPI:' + JSON.stringify(data.densityDPI)); 
-});
+} catch (exception) {
+    console.error('Failed to obtain the default display object. Code: ' + JSON.stringify(exception));
+} 
 ```
 
 ## How do I obtain the type of the device where the application is running?